Klim jerseys are an easy fit. For casual use (not wearing armor), choose the size you normally wear in men’s clothing and you’ll get a comfortable fit with some room left in it. Just to give you an idea, the size Small jerseys measure about 41” in the chest and 40” in the belly; size Large measures 44 chest/42 belly; size XXL measures 50 chest/48 max belly. These are all typical measurements in a standard men’s tee shirt.
If you will be wearing the jersey over protective gear, you’ll want to go up from the size you normally wear… probably one size. If you are unsure about how much to up-size, you can measure your chest and belly with and without your protective gear. Each additional 2” added to your chest/belly while wearing the gear, will require about one shirt size larger.